1. Field of the Invention
The present invention relates to an actuator using a strain element having such a property that it is deformed when voltage is applied, the so-called piezoelectric inverse effect, and a method of manufacturing the strain element.
2. Description of the Related Art
Conventionally, there has been an actuator using a piezoelectric element having such a property that a strain occurs and a deformation is caused when voltage is applied, the so-called piezoelectric inverse effect. In the actuator using the piezoelectric element, since an amount of deformation (amount of displacement) of the piezoelectric element is small, a mechanism portion (displacement enlargement mechanism portion) for enlarging the amount of displacement must be provided, and there has been a problem that its main body becomes large, and a problem that it takes labor to assemble the displacement enlargement mechanism portion.
Incidentally, the displacement enlargement mechanism portion is, as disclosed in Japanese Patent Unexamined Publication No. Hei. 4-25640, a mechanical enlargement mechanism portion employing the principle of leverage, a liquid type enlargement mechanism portion employing Pascal's principle, or the like.
Recently, an actuator in which the displacement enlargement mechanism portion is constructed by an actuator itself is proposed (Japanese Patent Unexamined Publication No. Hei. 6-216424). This actuator is constructed such that a belt-shaped piezoelectric element is helically wound over the full length of a hollow coil spring. According to this actuator, when voltage is applied to the piezoelectric element, a torsion moment by the deformation of the piezoelectric element acts on the full length of the coil spring, so that the coil spring is displaced in the axial direction. The amount of displacement of the coil spring in the axial direction can be made large if the number of turns of the coil spring is increased.
However, the actuator is assembled by helically winding the belt-shaped piezoelectric element over the full length of the hollow coil spring, and the step of helically winding the belt-shaped piezoelectric element is a very troublesome step, so that manufacturing costs are raised and the actuator is expensive.